i. Field of the Invention
The invention relates to a treatment of a thermoplastic polymer comprising, in the copolymerized form or in the grafted form, a monomer with an epoxide functional group and comprising the said monomer with an epoxide functional group in the free form, also known as residual monomer, that is to say not having reacted by copolymerization or by grafting. The treatment is intended to capture the said residual monomer. The invention also relates to the compositions and the blends comprising such thermoplastic polymers obtained by the said treatment.
ii. Description of the Related Art
Several techniques are already well known in industry for reducing the content of residual compounds in polymers. A degassing can, for example, be carried out in degassing silos fed with nitrogen or with hot air. The removal of the residual compounds can also be carried out in the molten state in devices known as devolatilizers, as is the case in the manufacture of polystyrene. In this case, the molten polymer is dispersed in a chamber maintained under high vacuum, the volatile components thus being entrained under the effect of the vacuum. The devolatilization can also be carried out in an extruder equipped with one or more degassing wells.
The document WO 98/25974 relates to a composition comprising an acid-based ethylene copolymer, such as ethylene/(meth)acrylic acid. This copolymer is blended with a hydrophilic zeolite (zeolite having an SiO2/Al2O3 ratio of less than 100, preferably of less than 35 and advantageously of less than 3; absorbing more than 10% of water at 25° C. under a pressure of 4.6 torr) so as to form a composition with a reduced content of residual monomeric acid which has not copolymerized and which is included in the polymer. In this document, no mention is made of a monomer with an epoxide functional group or of the colour of the copolymer+zeolite composition.
The document WO 92/13029 relates to a process for removing taste- and odor-generating substances from plastics. The molecules responsible for causing this trouble are not disclosed. Tests carried out with hydrophilic zeolites Sylosiv® 3A and 10A produce a weak effect as regards the removal of the substances responsible for tastes/smells, whereas the hydrophobic zeolites Abscent® give good results. In this document, no mention is made of a monomer with an epoxide functional group.
The document WO 92/13899 relates to a process for removing taste- and odor-generating substances from polyolefins. The molecules responsible for causing this trouble are not disclosed. Hydrophobic zeolites (zeolite having an SiO2/Al2O3 ratio of greater than 17, preferably of greater than 100; absorbing less than 10% of water at 25° C. under a pressure of 4.6 torr) are preferred.
Some compounds, including glycidyl methacrylate (GMA), are suspected of having a toxicological effect even in the form of trace amounts. International legislation is tending to become more restrictive regarding the level of residual compounds in polymers. The production of polymers comprising minute, indeed even zero, amounts of residual compounds is therefore proving to be an important challenge.
If the degassing technique is completely ineffective on polymer granules, the devolatilization technique in the molten state is more effective but does not make it possible to significantly reduce the amount of residual compounds. Furthermore, the solution consisting in installing a device of the vacuum devolatilizer type is a solution which demands a high capital cost.